For any application a user must consider a number of factors when choosing a tool material. Such factors including: cost; toughness; wear rate/hardness; ability to process a desired working surface such as a cutting edge; useful lifetime; required size and geometry; and inertness to chemical effects with the material to be processed.
An ideal tool material is one which is both hard and tough. These two properties of materials used in wear and tear applications are often presented on two perpendicular axes. Very simply, wear is a measurement of the amount of material removed per unit of operation. Toughness is a measure of a material's resistance to crack propagation. There is an on-going desire to provide materials which are harder, tougher, stronger and more wear resistant.
Diamond materials are the materials of choice for many premium performance cutting, drilling, grinding and polishing tools. Diamond materials are used in tooling solutions across a range of industries including a variety of metal, stone, electronics, and woodworking industries. Examples include aerospace and automotive manufacturing, furniture production, stone quarrying, construction, mining and tunnelling, mineral processing, electronic component and device fabrication, and the oil and gas industries. Examples of diamond tool parts include: wear parts; dressers; wire drawing dies; gauge stones; and cutters such as blades or other parts comprising a cutting edge.
Diamond's hardness properties make it the ultimate material in terms of wear. However, diamond's limited ability to plastically deform under stress at the tool's working temperature leads to more rapid crack propagation in comparison to much tougher materials such as steel. Previous attempts to improve the durability of diamond have involved either adapting the method of forming the diamond material, e.g. by varying nitrogen content, or treating the diamond material after forming the material, e.g. by irradiation and/or annealing. It has been found that such approaches can be used to improve the toughness and/or wear resistance of diamond tools.
Diamond tools usually comprise a diamond work piece mounted in a holder which may be fabricated, for example, using a metal material. The diamond work piece may be fabricated using a single crystal of natural, CVD synthetic, or HPHT (high pressure high temperature) synthetic diamond material. Alternatively, the diamond work piece may comprise a plurality of diamond grains bonded via a matrix of binder material, e.g. silicon cemented diamond, or via diamond-to-diamond bonding using a metal solvent, e.g. PCD (HPHT polycrystalline diamond) formed using a cobalt metal solvent, the latter usually containing residual metal solvent material although this can be leached out of the material after synthesis to a varying extent. Alternatively still, the diamond work piece may be fabricated using polycrystalline CVD synthetic diamond material which comprises a plurality of diamond grains directly bonded together via diamond-to-diamond bonding as a result of the CVD growth method, without the use of any metal solvent.
The aforementioned diamond materials have different physical characteristics and the type of diamond material used for a particular application will depend on the characteristics required for the application.
While many applications require a diamond material which has improved toughness and/or wear resistance as previously described, certain diamond tool applications require the ability to provide a very fine surface finish on the material being processed by the diamond tool. For example, metal device packaging for electronic devices may require a very fine surface finish for cosmetic purposes. Such applications also require a diamond tool part which has a working surface with certain minimum dimensions.
It is an aim of embodiments of the present invention to provide diamond tool parts which are capable of providing a very fine surface finish while also providing a working surface with sufficiently large dimensions as required for certain commercial applications.